1. Field of the Invention
This invention generally relates to an engine compartment structure. More specifically, the present invention relates to an engine compartment structure for a four-wheel drive vehicle.
2. Background Information
In the following descriptions, references to directions and orientations will be made with respect to the driving direction of a vehicle. Therefore, for instance, a xe2x80x9ctransverse directionxe2x80x9d means the direction of the width of the vehicle. Also, xe2x80x9cleft sidexe2x80x9d and xe2x80x9cright sidexe2x80x9d mean the left side and right side from the point of view of the driver.
In a conventional four-wheel drive (4WD) in which an engine unit is transversely mounted in the engine compartment, a front axle extends from a transaxle, and an output shaft protrudes rearward from a transfer case. The transaxle is an integrated unit that includes a transmission and an axle (drive shaft). The transfer case serves as an auxiliary transmission that is combined with the transaxle. Power is transferred from the output shaft to a rear axle via a propeller shaft. Japanese Laid-Open Utility Model Publication No. 3-126773 discloses an example of a similar arrangement.
The output shaft that extends rearward from the transfer case is positioned at the same height as the front axle. Therefore, the output shaft is located at a higher position than a surface of a floor panel. Consequently, the output shaft and the propeller shaft connected thereto are housed in a floor tunnel part, which is a convex portion of the floor panel protruding upward from the surface of the floor panel.
Side members that extend in a longitudinal direction of the vehicle are disposed on both left and right sides of the engine room. A rear portion of each of these side members is bent downward from an intermediate point so as to follow the contour of the bottom of a dash panel. A rear cross member is provided in a transverse orientation between the downwardly bent portions of the side members. A steering rack is mounted on the rear cross member. The steering rack thus mounted to the upper surface of the rear cross member is positioned under the output shaft.
In view of the above, there exists a need for an engine compartment structure for an improved four-wheel drive vehicle. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been found in this conventional arrangement, discussed above, that the position of the output shaft is relatively high. Consequently, the position of the floor tunnel, which houses the output shaft and the propeller shaft connected to the output shaft, also has to be high. As a result, the floor tunnel intrudes into the vehicle interior space, making the vehicle interior space smaller than it would be if the floor tunnel were not so high.
Also, it has also been found that since the position of the output shaft is high, the position of the steering rack that passes under the output shaft is also inevitably high. Consequently, the vertical space between the steering rack and the dash panel is small. As a result, the cross sectional height of the side members that pass through the space between the steering rack and the dash panel is small. Therefore, the only way to improve the front collision performance of the side members where the cross sectional height of the side members is small, is to increase the thickness of the material from which the side members are made. However, this tends to make press forming of the side members more difficult.
An object of the present invention is to provide a four-wheel drive vehicle the engine compartment structure in which the floor tunnel part is lowered and the cross sectional height of the side members is increased.
The aforementioned object can be attained by providing an engine compartment structure for a four-wheel drive vehicle, comprising a pair of longitudinal extending side members, a rear cross member, a steering rack and a four-wheel drive engine unit. The side members are disposed on left and right sides of the vehicle. Each of the side members has a rear portion. The rear cross member is disposed between rear portions of the side members and extends in a transverse direction of the vehicle. The steering rack is mounted on the rear cross member. The four-wheel drive engine unit includes an engine, a transfer case and a transaxle arranged to rotate a front axle. The transfer case has a rearward output shaft that transmits a driving torque for rotating a rear axle. The four-wheel drive engine unit is transversely disposed in the engine compartment structure. The output shaft has a center axis of rotation positioned lower than a center axis of rotation of the front axle of the transaxle. The steering rack is positioned lower than the output shaft.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.